Hot Tearing Evaluation and Contraction Behaviors of Four AA7xxx Alloys

Abstract

The hot tearing susceptibilities (HTS) of some AA7×××alloys, AA7050, AA7055, AA7085 and AA7022 were evaluated with constrained rod casting (CRC). Thermal contraction behaviors during solidification were measured as well in a T-shaped setup. The results showed that alloys with HTS from high to low were AA7055, AA7085, AA7050 and AA7022. Zn content in 7××× aluminum alloys seemed to play a major role with respect to the HTS index. Remarkable differences could be seen on thermal contraction behaviors within solidification range for each alloy. The rate and amount of thermal contraction for AA7055 was most prominent, followed by AA7085 and AA7050, while contraction curve of AA7022 was very flat together with least amount of thermal contraction. There was a well consistency between the amount of thermal contraction and HTS. Despite complex interactions of many variables in the formation of hot tear, thermal contraction behaviors within solidification range could give a quick evaluation of hot tearing susceptibility.

Effect of Main Elements (Zn, Mg, and Cu) on Hot Tearing Susceptibility During Direct-Chill Casting of 7xxx Aluminum Alloys

“…The rating of the amount of linear contraction for the four alloys is given as AA7022 < AA7050 < AA7085 < AA7055. [10] Here, this linear contraction is compared with the hot tearing predictions below. Compared with other alloys, AA7022 has the lowest Cu content and the highest Mg content, and its Zn content is closer to 4 to 6 wt pct.…”

“…[7][8][9] Besides these factors, alloy composition is another crucial point to affect the hot tearing susceptibility. Bai et al [10,11] investigated the hot tearing and thermal contraction behavior of several commercial 7xxx alloys. It was found that different alloys exhibited different hot tearing resistance.…”